Well back to the real VDU - something to watch out for - in my pursuit of learning how to control the VDU from the 8154 I have somehow fried a bit of IC1 74L86 (Quad exclusive OR - the gate on pins 1,2,3) these control the ReversePages Input and TopPage Output. I bought this from Martin when I bought the PCB as it is NOT the same as the 74LS86 pinout - two of the gates have the output and one input reversed:
I have paid the LittleDiode premium to (hopefully) get a replacement in a few days - however, if anyone has a similar problem I just bent out Pin 3 which was grounding the TopPage Output line and tapped into Pin 2 from IC6 (Pin 15 on the 4040) - this means you cannot have the F00 at the top which is better as the first line is not visible. But, it will do to allow the whole of RAM to be visible for the moment.